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From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: copy on write
Date: Thu, 02 Feb 2012 12:25:00 -0500
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On 2/2/2012 9:17 AM, John O'Hagan wrote:

> It's not so much about the type of x but that of x[1]. Wouldn't it be
> possible to omit the assignment simply if the object referred to by
> x[1] uses "+=" without creating a new object? That way, some_tuple[i]
> += y will succeed if some_tuple[i] is a list but not with, say, an
> int. That seems reasonable to me.

There was considerable discussion of the exact semantics of augmented 
operations when they were introduced. I do not remember if that 
particular idea was suggested (and rejected) or not. You could try to 
look at the PEP, if there is one, or the dicussion ( probably on pydev 
list).

-- 
Terry Jan Reedy